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References: <20231205085959.32177-1-zong.li@sifive.com>
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From: Zong Li <zong.li@sifive.com>
Date: Fri, 29 Dec 2023 14:34:43 +0800
Message-ID: <CANXhq0r6A48q+ehayaURLO6snDEjzVJO6Ti+1we-57i0ORT9yg@mail.gmail.com>
Subject: Re: [PATCH] riscv: add CALLER_ADDRx support
To: palmer@dabbelt.com, paul.walmsley@sifive.com, aou@eecs.berkeley.edu, 
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
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On Tue, Dec 5, 2023 at 5:00=E2=80=AFPM Zong Li <zong.li@sifive.com> wrote:
>
> CALLER_ADDRx returns caller's address at specified level, they are used
> for several tracers. These macros eventually use
> __builtin_return_address(n) to get the caller's address if arch doesn't
> define their own implementation.
>
> In RISC-V, __builtin_return_address(n) only works when n =3D=3D 0, we nee=
d
> to walk the stack frame to get the caller's address at specified level.
>
> data.level started from 'level + 3' due to the call flow of getting
> caller's address in RISC-V implementation. If we don't have additional
> three iteration, the level is corresponding to follows:
>
> callsite -> return_address -> arch_stack_walk -> walk_stackframe
> |           |                 |                  |
> level 3     level 2           level 1            level 0
>
> Signed-off-by: Zong Li <zong.li@sifive.com>
> ---
>  arch/riscv/include/asm/ftrace.h    |  5 ++++
>  arch/riscv/kernel/Makefile         |  2 ++
>  arch/riscv/kernel/return_address.c | 48 ++++++++++++++++++++++++++++++
>  3 files changed, 55 insertions(+)
>  create mode 100644 arch/riscv/kernel/return_address.c
>
> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftr=
ace.h
> index 2b2f5df7ef2c..42777f91a9c5 100644
> --- a/arch/riscv/include/asm/ftrace.h
> +++ b/arch/riscv/include/asm/ftrace.h
> @@ -25,6 +25,11 @@
>
>  #define ARCH_SUPPORTS_FTRACE_OPS 1
>  #ifndef __ASSEMBLY__
> +
> +extern void *return_address(unsigned int level);
> +
> +#define ftrace_return_address(n) return_address(n)
> +
>  void MCOUNT_NAME(void);
>  static inline unsigned long ftrace_call_adjust(unsigned long addr)
>  {
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index fee22a3d1b53..40d054939ae2 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -7,6 +7,7 @@ ifdef CONFIG_FTRACE
>  CFLAGS_REMOVE_ftrace.o =3D $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_patch.o  =3D $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_sbi.o    =3D $(CC_FLAGS_FTRACE)
> +CFLAGS_REMOVE_return_address.o =3D $(CC_FLAGS_FTRACE)
>  endif
>  CFLAGS_syscall_table.o +=3D $(call cc-option,-Wno-override-init,)
>  CFLAGS_compat_syscall_table.o +=3D $(call cc-option,-Wno-override-init,)
> @@ -46,6 +47,7 @@ obj-y +=3D irq.o
>  obj-y  +=3D process.o
>  obj-y  +=3D ptrace.o
>  obj-y  +=3D reset.o
> +obj-y  +=3D return_address.o
>  obj-y  +=3D setup.o
>  obj-y  +=3D signal.o
>  obj-y  +=3D syscall_table.o
> diff --git a/arch/riscv/kernel/return_address.c b/arch/riscv/kernel/retur=
n_address.c
> new file mode 100644
> index 000000000000..c2008d4aa6e5
> --- /dev/null
> +++ b/arch/riscv/kernel/return_address.c
> @@ -0,0 +1,48 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * This code come from arch/arm64/kernel/return_address.c
> + *
> + * Copyright (C) 2023 SiFive.
> + */
> +
> +#include <linux/export.h>
> +#include <linux/kprobes.h>
> +#include <linux/stacktrace.h>
> +
> +struct return_address_data {
> +       unsigned int level;
> +       void *addr;
> +};
> +
> +static bool save_return_addr(void *d, unsigned long pc)
> +{
> +       struct return_address_data *data =3D d;
> +
> +       if (!data->level) {
> +               data->addr =3D (void *)pc;
> +               return false;
> +       }
> +
> +       --data->level;
> +
> +       return true;
> +}
> +NOKPROBE_SYMBOL(save_return_addr);
> +
> +void *return_address(unsigned int level)
> +{
> +       struct return_address_data data;
> +
> +       data.level =3D level + 3;
> +       data.addr =3D NULL;
> +
> +       arch_stack_walk(save_return_addr, &data, current, NULL);
> +
> +       if (!data.level)
> +               return data.addr;
> +       else
> +               return NULL;
> +
> +}
> +EXPORT_SYMBOL_GPL(return_address);
> +NOKPROBE_SYMBOL(return_address);
> --
> 2.17.1
>

Hi Palmer and all,
I was wondering whether this patch is good for everyone? Thanks